TNT, Nanotubes And A Laser Lighter Can Mean Efficient Power Generation

It was four years ago that researchers at the MIT assembled a piece of yarn out of carbon nanotubes, coated it with TNT and lit it with a laser. Predictably it burned like a dynamite fuse, thus demonstrating it could generate enormous amounts of electricity.

But there was one problem: No one could figure out how the process worked. Michael Strano, the head of the lab where the light was lit, told the MIT Technology Review that at the time it was so inefficient he feared it would end up as just another “laboratory curiosity.”

That was then. Now, Strano says, he’s figured out the physics behind this burning fuse, and as a result his team has improved the efficiency of the device by 10,000 times. Eventually, he says, the method could lead to portable electronic devices that last longer and even make electric cars more convenient by shortening their refueling time and extending their mileage on a single charge.

But this is still now, Strano stresses. The current efficiencies of the process are still low. The efficiency of conventional generators today is between 25 percent and 60 percent; his nanogenerator has an efficiency of just over 0.1 percent.

The MIT team is working to improve the nanogenerator’s efficiency factor to make it work in general applications, but until then, Strano says, it could be useful in certain applications requiring occasional short bursts of power.

Strano explains that his team’s generator makes use of a phenomenon that he calls a “thermopower wave.” In a conventional fuel-burning generator, he says, the heat of combustion causes gases to expand and drive a piston or a turbine. In the MIT nanogenerator, as the flame burns a liquid fuel along the length of the fuse, it drives electrons ahead of it to create an electrical current.

The fuel, of course, must be non-polluting. Strano tells the online journal Transport Evolved that his team has been using clean-burning fuels including ethanol, sugar and even formic acid, extracted from fire ants.

The MIT nanogenerator isn’t just an alternative to, say, a coal-fired generator. In fact, it’s more efficient, Strano says, because it involves no pistons or turbines. What’s more, its liquid fuels have a higher energy storage capacity than conventional batteries. As a result, they could store enough electricity to give electric cars greater range than they have today.

As novel as the nanogenerator is, it’s not entirely unlike the conventional internal-combustion engine. In current automotive technology, the engine sprays tiny bursts of fuel into combustion chambers, where the fuel explodes and powers pistons.

According to Strano, multiple MIT-style nanogenerators could feed bursts of power to electronic circuits, which would even out the bursts to create a steady flow of electricity for a smooth car ride. Further, the car’s fuel tank could be filled as quickly and easily as if it were a conventional fuel tank.The best part is that the nanotubes aren’t burned up in the process of generating electricity, so they can be used indefinitely.

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